1. Field of the Invention
The present invention relates generally to gerotor hydraulic devices that can be used as pumps or motors and, more particularly, to such devices having a rotary valve plate therein.
2. Description of the Prior Art
Many types of prior art hydraulic devices have utilized internal gear sets which are often called gerotors or rotors. Such devices can be used as pumps where shaft work is converted to hydraulic work and as motors where hydraulic work is converted to shaft work. Examples of gerotor pumps and motors are shown in U.S. Pat. Nos. 3,572,983; 4,411,607; 4,545,748; and 4,586,885. In an internal gear pump or motor, an inner gear having outwardly directed teeth cooperates with an external gear having inwardly directed teeth so that fluid chambers therebetween increase and decrease in volume as the inner and outer gears rotate in a housing. By connecting the inlet and outlet of the device to the proper location along the sides of the gear set, the variable displacement chambers receive and discharge hydraulic fluid so that the device can function as a pump or motor. A shaft or other mechanical device can be connected to either the inner or outer gear depending upon the type of device.
Many of the internal gear pumps and motors of the prior art utilize a housing having a fixed inlet and outlet. In other gerotor pumps and motors, a rotary valve plate or disc is used. An example of gear devices with a rotary valve plate are shown in U.S. Pat. Nos. 4,411,607; 4,545,748; 4,586,885; and applicant's co-pending U.S. patent application No. 860,715, filed May 6, 1986 now U.S. Pat. No. 4,699,577. As described in these patents, the internal gear devices with rotary valves have a control plate or commutator with a plurality of inlet and outlet openings or windows on an axial face thereof. A valve plate with a plurality of openings extending axially therethrough is disposed between the gear set and the commutator to selectively communicate the inlet and outlet openings with the variable displacement chambers in the gear set. The valve plate is connected to rotate with the gear set such that the closing variable displacement chambers in the gear set are connected with the outlet openings of the commutator while the opening variable displacement chambers of the gear set are connected with the inlet.
A well known problem which occurs in devices with rotary valve plates is that the valve plate is subject to a tilting moment caused by high pressure fluid bearing against one radial half of the valve plate, while low pressure fluid bears against the other radial half of the valve plate. In addition, there is a relatively larger area of pressure bearing on the gear set side of the valve plate than on the commutator side of the valve plate. The combination of this pressure imbalance reduces the efficiency and operational life of the device by increasing friction and wear on the moving components.
A partial solution to the imbalance is shown in U.S. Pat. No. 4,411,607. In this patent, recesses and grooves are provided on the rotary valve face on the commutator side of the rotary valve plate. These recesses provide a greater fluid pressure area on the commutator side of the valve plate to counterbalance the normally greater area of fluid pressure on the gear set side of the valve plate. However, the imbalance of high pressure from the commutator ports on one radial half (commutator side) of the valve plate versus low pressure on the same radial half (gear set side) partially remains.
In applicant's co-pending patent application Ser. No. 860,715 a further means of balancing the imbalance is shown. This is achieved by ports which extend through the valve plate to communicate high pressure fluid on the commutator side of the valve plate to a peripheral groove on the low pressure gear set side of the valve plate. These ports are selectively communicated with the high pressure in the commutator openings by the rotation of the valve. Thus, the radial half of the control plate which is not balanced due to high pressure commutator ports being opposite low pressure displacement chambers in the gear set are balanced by an area of high pressure fluid on the gear set side communicated through the special ports. However, some leakage of this high pressure fluid into the low pressure variable displacement chambers in the gear set occurs causing a reduction in efficiency of the motor or pump which would not occur if the leakage were not present. Further, this solution is not possible on machines where the outer rotor orbits as opposed to the inner rotor orbiting.
It is accordingly an object of the present invention to provide an internal gear motor or pump with an improved means of balancing the hydraulic pressures on the rotating valve plate. It is also an object of the present invention to provide a valve plate which is of simple construction and which prevents or reduces leakage from the commutator side of the valve plate to the gear set side of the valve plate. It is, still further, an object to provide such improvements for an internal gear machine of the type having an orbiting outer gerotor.